Method and apparatus for separating granular goods

ABSTRACT

In a method of separating granular goods of different specific gravity, by separating the goods, by a forced air flow therethrough while the goods are on a goods support subjected to a vibration, into a layer of heavier fractions and a layer of lighter fractions, separating the layers and separately discharging the layers, the goods are pre-sorted, in advance of charging thereof onto the support, into a bottom layer, enriched with the heavy fractions, and a superposed layer, free of the heavy fractions. The two layers, while in such superposed relation, are then charged onto the goods support. The apparatus includes a goods feeding device, for pre-sorting of the goods, in the form of a vibrating duct having a gas permeable bottom wall. The duct forms an initial sedimentation path of the heavy fraction of the goods, and the discharge end of the duct is spaced from the outlet for the heavy fraction to form a succeeding sedimentation path of the heavy fraction charged onto the goods support.

[451 Sept. 26, 1972 METHOD AND APPARATUS FOR SEPARATING GRANULAR GOODS[72] inventor: Hans Oetiker, Gallen, Switzerland [73] Assignee: GebruderBuhler AG, Gallen, Switzerland 22 Filed: April 17,1969 21 Appl.No.:817,127

[30] Foreign Application Priority Data April 17, 1968 Switzerland..5678/68 Nov. 17, 1968 Switzerland ..16799/68 [52] US. Cl. ..209/467,209/490, 209/497 [51] Int. Cl. ..B07b 3/10 [58] Field of Search ..209/3,424, 426, 442, 456, 209/460, 467, 469, 472, 474, 476, 477, 481, 486,497, 466, 468

2,852,137 9/1958 Hagopian ..209/139 R 3,045,825 7/1962 Watson ..209/471FOREIGN PATENTS OR APPLICATIONS 333,622 8/ 1930 Great Britain ..209/467Primary Examiner-Frank W. Lutter Assistant ExaminerRalph J. HillAttorney-McGlew and Toren [5 7] ABSTRACT In a method of separatinggranular goods of different specific gravity, by separating the goods,by a forced air flow th'erethrough while the goods are on a goodssupport subjected to a vibration, into a layer of heavier fractions anda layer of lighter fractions, separating the layers and separatelydischarging the layers, the goods are pre-sorted, in advance of chargingthereof onto the support, into a bottom layer, enriched with the heavyfractions, and a superposed layer, free of the heavy fractions. The twolayers, while in such superposed relation, are then charged onto thegoods support. The apparatus includes a goods feeding device, forpre-sorting of the goods, in the form of a vibrating duct having a gaspermeable bottom wall. The duct forms an initial sedimentation path ofthe heavy fraction of the goods, and the discharge end of the duct isspaced from the outlet for the heavy fraction to form a succeedingsedimentation path of the heavy fraction charged onto the goods support.

30 Claims, 6 Drawing Figures PATENTEDSEPz I912 3,693,794

SHEET 2 BF 6 4 TTURME/f PATENTED 8EP26 m2 3 6 93, 7 94 SHEET 6 BF 6 Fig.6

METHOD AND APPARATUS FOR SEPARATING GRANULAR GOODS BACKGROUND OF THEINVENTION uniformly distributed manner, and thus to mix the lo materialin a material-air mixture which flows, in a floating manner, in thedirection of descent of the inclined surface. The heavy fractionsseparate from the light fractions and sink gradually toward the surface.In order to separate these heavy fractions from the superposed lightfractions, the surface is vibrated in a direction opposite to the lineof descent, so that the heavy fractions are moved in the direction ofvibration and separated from the flowing material-air mixture or screen.

The paths along which the separation into light and heavy fractions iseffected in the current of goods will hereinafter be called thesedimentation paths. This path depends on the difference between thespecific gravities of the light and heavy fractions, on the height ofthe goods current, on its velocity of flow and on the type of granulargoods. In these devices, such as shown in U.S. Pat. Nos. 2,404,414,2,040,196, 2,427,423, 2,718,306 and 2,928,545, the mixed fractions arecharged onto the inclined goods support between a discharge device andthe outlets.

In order to obtain a uniform distribution of the mixed fractions on theinclined goods support, the feed is effected in a falling mist extendingsubstantially throughout the entire width of the goods support. All ofthese devices have the disadvantage that the air cushion, formed on theinclined goods support, is irregular, due to turbulence and differentheights of the charge of goods. As a result, the air-goods current andsedimentation of the heavy fractions, that is, their sinking to thegoods support, is disturbed, so that separation is inefficient. Anotherdisadvantage is that the heavy fractions, sedimented down to the goodssupport and which are to slide, under the action of the vibratorymovement of the goods support, in a direction opposite to the line ofdescent and extending to the outlet, must be moved under theabove-mentioned falling mist. Due to the turbulence of the air-goodscurrent, occurring in the range of the falling mist, the heavy fractionsare again carried along by the air-goods current, which has the sameresult in that separation is insufficient and inefficient.

Other devices for separating granular goods according to differentspecific gravity are known, for example, those shown in US. Pat. No.2,718,307 and British Pat. No. 293,472. These devices also use avibrating and inclined air-permeable goods support. These devices alsoinclude an air feeding arrangement directed beneath the goods and towardthe goods for the formation of an air-goods mixture, but the feeding ofthe mixed fractions takes place in the range of the lowest point andadjacent a lateral boundary of the goods support. The vibratory movementof the goods support likewise is effected in the direction opposite tothe line of descent, but separating elements are provided by means ofwhich the separating fractions are directed to the side of the goodssupport opposite the goods feed, and are there recovered. ln order toattain a satisfactory separating effect, those obtained fractions whichare between the lightest and the heaviest fractions are returned, in acycle, to the goods feed and charged onto the vibrating goods support.This has the result that the capacity of these devices is very low.

SUMMARY OF THE INVENTION This invention relates to the separation ofgranular goods of different specific gravity and, more particularly, toan improved, simplified and more efficient method and apparatus foreffecting such separation.

The invention is directed to a method for separating granular goods ofdifferent specific gravity, in which the granular goods are separated ina forced air current while on a support which exerts a vibration on thegoods, the goods being separated into a layer of heavy fractions and alayer of light fractions. The goods are then separated and dischargedthrough respective outlets. The invention is further directed toapparatus for separating granular goods in accordance with specificgravity, and including a vibrating and inclined airpermeable goodssupport, an oppositely directed air feeding device arranged beneath thesupport, at least one outlet for the heavy fraction arranged at thehighest point of the support, a discharge device for the light fractionarranged at the lowest point of the support, and a goods feeding devicearranged in between the discharge device and the outlet and opening ontothe support.

In accordance with the invention, before the granular goods are chargedonto the goods support, the goods are pre-sorted into a bottom layer,enriched with the heavier fractions, and a superposed layer, which isfree of the heavy fractions. The superposed layers, without change, arethen charged onto the material support. For performing the inventionmethod, the goods feeding device is designed as a vibrating duct with agas-permeable bottom wall, this duct, up to its discharge end, formingan initial sedimentation path of the heavy fraction of the suppliedgoods, and the discharge end of duct is spaced from the outlet to form asucceeding sedimentation path of the heavy fraction as charged onto thegoods support.

An object of the invention is to provide an improved method of andapparatus for separating granular materials at different specificgravities.

Another object of the invention is to provide such a method andapparatus in which the separation is effected in a simpler, moreeconomical and more efficient manner.

A further object of the invention is to provide such a method andapparatus in which, in advance of charging of the goods onto a materialsupport which is vibrated in a goods-advancing direction, with the goodsbeing subjected to a forced air flow while on the support, the goods arepre-sorted into a bottom layer enriched with the heavier fractions and asuperposed layer which is free of the heavy fractions.

Another object of the invention is to provide such a method andapparatus in which the still superposed but separated layers are chargedonto the goods support.

A further object of the invention is to provide such a method andapparatus in which a goods feeding device is designed as a vibratingduct having a gas-permeable bottom wall.

A further object of the invention is to provide such a method andapparatus in which this duct forms an initial sedimentation path of theheavy fraction of the material supplied, and in which the discharge endof the duct is spaced from the heavy fraction outlet to form asucceeding sedimentation path of the heavy fraction as charged onto thegoods support.

For an understanding of the principles of the invention, reference ismade to the following description of typical embodiments thereof asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a longitudinal sectional view through a first embodiment ofapparatus in accordance with the invention;

FIG. 2 is a top plan view of the embodiment shown in FIG. 1, with partsbeing cutaway;

FIG. 3 is a longitudinal sectional view through a second embodiment ofapparatus in accordance with DESCRIPTION OF THE PREFERRED EMBODIMENTS Inthe embodiment of the invention shown in FIGS; 1 and 2, an air-permeablegoods support 1 is arranged in the casing 2 and rigidly connectedlengthwise with this casing. Support 1 comprises a screen 3 beneathwhich is arranged, in parallel relation therewith, a perforated plate 4.Perforated plate 4 is formed with circular apertures, whose diameter andspacing is dimensioned in accordance with the required velocity of theair passing through the goods support 1. Baffles 5 are disposed betweenH screen 3 and plate 4 to form rectangular panels, and these baffles arebonded, along their relatively narrow upper and lower edges, to screen 3and plate 4, respectively.

The design of goods support 1 is very important for satisfactoryoperation of the apparatus for separating granular goods, since theaction of the air, on the goods to be separated, can be influenced bythe suitable selection of the perforations in plate 4 and of the baffles5 extending between screen 3, which serves'as a porous material support,and perforated plate 4. Toward the range of its highest point, support 1is tapered and converges into an outlet 6 having associated therewith anelastic tube 11, having a narrow or slit-type outlet, through which theheavy fraction is discharged.

It has been found that the side wall for bounding the separating surfaceabove the goods support, and converging toward the outlet 6, shouldextend at an angle a, with respect to the transverse axis of the goodssupport, whose tangent is not less than 1.8 but preferably is between 2and 3. In this embodiment of the invention, this results in a goodssupport which is triangular in plan and whose boundaries form,approximately, angles of 30, 60 and with each other. In the range of thelowest point of support 1, the latter is terminated by a rib 7 extendingtransversely of the line of descent of the support. The height of rib 7limits the height of the layer of granular goods charged onto the goodssupport, and this layer drops over rib 7 into a discharge device 8.Device 8 is bounded laterally by the walls of easing 2 and by the rib 7,and is tapered downwardly to a nipple 9 to which is connected an elastictube 10 which forms a slit-shaped outlet opening at its free end.

Beneath'support 1, casing 2 forms a free chamber 12 which tapers to anipple 13 which is connected, through a tubular collar 14 and a conduit15 with a compressed air source 16. Casing 2, to which support 1 isfixedly connected along its outer, edges, is supported on flexibleresilient supports 17. A vibrator 18 is arranged on an end face ofcasing 2, and this vibrator includes a motor 19 having an eccentricweight 20 secured on its driven or output shaft. Toward its upper end,casing 2 is closed by a cover plate 21 which has a sight glass 42extending at least in the range of outlet 6. Cover plate 21 has a nipple22 which connects the free space above support 1 and, through a tubularcollar 23, with an air exhaust which has not been shown. A laterallyextending sleeve 24 is connected with collar 23, and its outer end canbe closed by an elastic ring 25. By' virtue of the provision of sleeve24, which may be termed an arm sleeve, the free space above support 1 isaccessible to an operator standing outsidethe apparatus.

The goods feeding device is formedby a duct 26 having a closed front endinto'which opens a vertical feed pipe 27. Duct 26 is bounded laterallyby a side wall of casing 2 and by a partition 28, the end of partition.28 forming, with the side wall of casing 2, a discharge end or mouth 40for duct 26. Duct 26, from its head, beneath the discharge end of feedpipe 27, to its mouth 40, forms an initial sedimentation path. Dischargeend or mouth 40 of duct 26 is spacedfrom outlet 6 and from dischargedevice 8, in the direction of movement of goods along support 1, to forma succeeding sedimentation path, so that the-length of support1,-measured in the direction of its line of descent, is at least doublethe length of such succeeding sedimentation path. The bottom wall ofduct 26 is formed by a part of support 1. Partition 28 has an opening 29spaced somewhat from mouth 40, and opening 29 opens in a directiontransversely of the line of descent of support 1. Opening 29 has astraight bottom edge 30 which is inclined in a direction toward outlet6.

An air blast nozzle 32, having a nozzle end extending in the directionof descent of support 1 and substantially parallel to the latter, issupplied with air under pressure through a conduit 31 connected to anair source whose pressure is higher than the pressure in casing 2beneath cover plate 21.

The invention apparatus operates in a manner which will now bedescribed. Goods support 1, which is mounted on the oscillatablesupports 17, is operatively associated with vibrator 18in a manner suchthat support 1 vibrates substantially parallel to the line of descent,the vibrations acting to advance goods on support 1 upwardly towardoutlet 6. Y Compressed air source 16 supplies compressed air throughline 15, tu-

bular collar 14, and nipple 13 beneath perforated plate 4. Thecompressed air flows through the apertures in plate 4 into the panelsformed between plate 4 and screen 3 by baffles 5. Baffles 5 insure auniformly distributed air flow through screen 3 in the volume formedabove screen 3 by easing 2, the air leaving this volume through nipple22 and tubular exhaust collar 23.

The mixed fractions of the granular goods are introduced through feedpipe 27 into duct 26, and float, as an air-goods mixture, on screen 3toward duct opening 29, with the heavy fractions moving downwardlytoward screen 3 due to their higher specific gravity. When the heavyfractions reach screen 3 they receive, through the vibration of support1, an additional motion component directed oppositely to the descendinggradient of support 1, so that the heavy fractions move along duct 26and beyond the end of partition 28 into the range of outlet 6. The lightfractions flow over the lower edge 30 of opening 29 and onto goodssupport 1.

The special design of the air-permeable goods support 1, formed byscreen 3, baffles 5 and perforated plate 4, insures that the amount ofair acting on the goods to be separated is within 95 to 125 percent of avalue called the critical threshold value. This critical threshold valuecharacterizes the state wherein the material is above air permeablescreen 3 as an homogeneous, bubble-free fluidization layer, or airgoodsmixture, flowing in the manner of a liquid. This air-goods mixture isuniformly distributed over the support surface. The light fractions flowin the direction of the steepest inclination, in the manner of a liquid,toward rib 7 where they are restrained. If the height of the lightfractions floating on support 1 exceeds the height of rib 7, the lightfractions flow over the upper edge of rib 7 into discharge device 8 andleave the discharge device 8 through nozzles 10 which transfer the lightfractions of the granular goods to a sluice 33 driven by a motor 32.

If heavier fractions of the granular goods are still associated with thelight fractions passing through opening 29, these heavier fractions havea further opportunity, until the mixture reaches rib 7, to drop to thescreen 3 due to the higher specific gravity. On screen 3, the heavierfractions receive a goods advancing vibrational force directed towardoutlet 6, so that they move toward this outlet and through the lightfractions in counter flow to the direction of flow of the lightfractions. The movement of the heavy fractions, to be separated throughthe outlet 6, in the range of the converging side wall is influencedgreatly by the inclination of the side wall relative to the shortestdistance between outlet 6 and the discharge device 8 for the lightfractions. The tangent of the angle a of the inclined side walltherefore should be equal to or greater than 1.8.

The heavy fractions sinking in duct 26 below the lower edge 30 ofopening 29 pass the end of partition 28 through mouth 40 and ontosupport 1. If this heavy fraction still contains light fractions of thegranular goods, the light fractions spread over support 1 as anair-goods mixture and float in the direction of descent of support 1toward discharge device 8, while the heavy fractions continue to movetoward outlet 6.

In the embodiment of the invention shown in FIGS. 1 and 2, the mixedfractions are pre-sorted initially in duct 26, and into a bottom layerenriched with the heavy fractions and a superposed layer which is freeof the heavy fractions. The goods are subsequently charged, as these twosuperposed layers, onto goods support 1. After the pre-sorted andlayered fractions have been transferred to support 1, the layers areseparated and discharged through the respective outlets. Any parts ofthe light fraction which come into the range of outlet 6 are moved,under the action of the air jet issuing from nozzle 32 and directedalong the line of descent of support 1 toward discharge device 8, sothat passage of the light fractions into outlet 6 is practicallyimpossible.

In the second embodiment of the invention, shown in FIGS. 3 and 4, partsidentical with those of the embodiment shown in FIGS. 1 and 2 have beengiven the same reference number and will not be described further indetail. As best seen more particularly in FIG. 4, the airpermeable goodssupport 1, in plan, is shaped somewhat differently than in theembodiment of FIGS. 1 and 2. Duct 260 of the goods feeding device is nolonger arranged at one side of support 1, but extends symmetrically ofthe longitudinal axis of the latter. Duct 260 is bounded laterally bypartitions 280 and 281, and is divided into a front region and a rearregion which have different bottom inclinations. The rear region,beginning under the discharge end of feed pipe 27, is inclineddownwardly toward goods support 1 in order to accelerate discharge ofthe mixed goods. The front region of duct 260 has a bottom which iscoplanar with goods support 1, so that, in this front region, the goodsmove in a rising manner in a direction opposite to the line of descentof support 1.

The bottom of duct 260 in the rear region has the same design as support1, and comprises a perforated plate 44 which is fixedly connected with ascreen 30 by baffles 50. The length of duct 260 is selected so that afirst separation between the light fractions and the heavy fractions iseffected in the duct along an initial sedimentation path, as in theembodiment of FIGS. 1 and 2. Partitions 280 and 281 have, at their freeends, a stepped recess corresponding to the opening 29 of the embodimentof FIGS. 1 and 2, so that limiting edges 300 and 301, respectively, areformed. The goods, which have already been freed of the heavy fractionsin duct 260, can pass over these edges onto goods support 1, while anymixed fractions, as well as the heavy fractions leave duct 260 only inthe range of mouth 40 and then pass onto goods support 1.

FIGS. 5 and 6 illustrate a third embodiment of the invention, in whichit is possible to obtain a greater separating effect than in theembodiments shown in FIGS. 1 through 4. The air-permeable goods supportI is again positioned in casing 2 and fixedly connected with the latterlongitudinally. Support 1 comprises screen 3, perforated plate 4 andbaffles 5, which are firmly bonded to each other so as to form a unit.The side walls of support 1 can both converge toward the range of thehighest point thereof, and lead to the outlets 6 and 60 through whichthe heavy fraction is discharged. The two side walls of easing 2 havethe same angle of inclination a, and the tangent of the angle a again isequal to or greater than 1.8.

Support 1 is bounded, at its lowest point, by rib 7 over which the lightfraction flows into discharge device 8. Discharge device 8 has nipples 9to each of which is connected an elastic tube 10 through which the lightfraction is discharged into a sluice 33 of a pneumatic conveyor system.Chamber 12, beneath support 1, is connected to compressed air' source 16through nipple 13, tubular collar 14 and conduit 15. Casing 2 is mountedon the oscillatable resilient supports 17.

Vibrator 18 is secured on casing 2 and includes a motor 19 and aneccentric weight 20 driven by the motor. Casing 2 is closed, at itsupper end, by cover plate 21 formed with a nipple 22 to which there isconnected the tubular collar 23 leading to an air exhaust.

The material feeding device comprises a duct 260 into which a verticalfeed pipe 27 discharges, and duct 260, as best seen in FIG. 6, extendssymmetrically with respect to the plane of symmetry of support 1. Thisduct is bounded laterally by partitions 280 and 281, and its bottom isinclined toward support 1. The bottom of duct 260has the sameconstruction assupport 1, and comprises a perforated plate 44, which isfirmly bonded with screen '30through the medium of baffles 50. Thelength of duct 260 is selected so that an initial separation between theheavy fractions and a large part of the light fractions is effected inthe duct along an initial sedimentation path. Mouth 40 of duct 260 isspaced from outlets 6 and 60, and from discharge device 8, in thedirection of the line of descent of support 1, to form a succeedingsedimentation path. The length of support 1, measured in the directionof its line of descent, is thus at least double the length of suchsucceeding sedimentation path.

A wedge 34 is secured on screen 3 and, as best seen in FIG. 6, isarranged symmetrically relative to the plane of symmetry of support 1and has its pointed or tapered edge extending into the range of mouth 40of feeding device 260. In the ranges of the intersections of the flanksof wedge 34 with the converging side walls of easing 2, there arearranged respective outlets 6 and 60 through which the heavy fraction ofthe goods is discharged. Due to the flanks of wedge 34, the goodsissuing from duct 260 are positively deflected laterally and distributeduniformly over goods support 1. The greater uniformity in thedistribution of the goods on support 1 results in an increasedseparating effect of the apparatus.

, In a further embodiment of the invention, which has not beenillustrated as it is believed that it will be readily understandable toone skilled in the art, duct 26 or 26d of the goods feeding device iscompletely separated from goods support 1 and provided with a separatevibrating drive. In this case, the duct extends transversely of the lineof descent of goods support 1 and dischargescentrally onto thesupport 1. The limiting edges or 300 can be directed toward dischargedevice 8, while the duct 26 or 260, for the mixed and heavy fractions,has a discharge mouth directed transversely to the line of descent ofsupport 1, or toward the outlet 6.

In each of the above-described embodiments, the compressed air sourcecan be eliminated by exhausting air above goods support 1 whileproviding a free opening to atmosphere beneath perforated plate 4.

What is claimed is:

1. In a method of separating granular goods of different specificgravity, wherein the granular goods are separated, by a forced air flowtherethrough while the goods are on a goods support subjected to avibration, into a layer of heavier fractions and a layer of lighterfractions, the layers are separated, and the layers are separatelydischarged: the improvement comprising the steps of, in advance ofcharging the granular goods onto the support, pre-sorting the goods intoa bottom layer, enriched with the heavy fractions, and a superposedlayer, free of the heavy fractions; subsequently flowing the layeredpre-sorted material onto the support as a continuous current, with atleast the layer enriched with heavy fractions having a laminar flow; onthe support, separating the two layers to flow along the support insubstantially opposite respective directions; and separately dischargingeach layer.

2. In a method of separating granular goods of dif-,

ferent specific gravity, the improvement claimed in claim 1, includingthe step of conducting the continuous current along a laterally confinedpath which is coplanar with the goods support.

3. In a method of separating granular goods of different specificgravity, the improvement claimed in claim 1, including subjecting atleast one of the fractions to substantially a reversal in flow directionwhen charged onto the goods support.

4. In a method of separating granular goods of different specificgravity, wherein the granular goods are separated, by a forced air flowtherethrough while the goods are on a goods support subjected to avibration, into a layer of heavier fractions and a layer of lighterfractions, the layers are separated, and the layers are separatelydischarged: the improvement comprising the steps of, in advance ofcharging the granular goods onto the support, pre-sorting the goods intoa bottom layer, enriched with the heavy fractions, and a superposedlayer, free of the heavy fractions; maintaining such superposed relationwhile subsequently charging the two layers onto the goods support; thelayered presorted material being flowed onto the support as a continuouscurrent, with at least the layer enriched with heavy fractions having alaminar flow; conducting the continuous current along a laterallyconfined path which is coplanar with the goods support; and laterallydischarging at least a part of the superposed layer, free of the heavyfractions, from the path onto the goods support in advance of thedischarge end of the path.

5. In apparatusfor separating granular goods of different specificgravity, and of the type including an inclined gas-permeable goodssupport, means directing a gas current upwardly through the support, anoutlet for the heavy fractions at one end of the support, a dischargedevice for the light fractions at the other end of the support, thesupport having a gradient which descends from the outlet to thedischarge device and being vibrated in a direction opposite to thedescending gradient, and a goods feeding device discharging ontothegoods support: the improvement comprising, in combination, avibrating duct, having a gas-permeable bottom and a discharge mouth,included in said feeding device; means directing a gas current upwardlythrough said gas-permeable bottom; said duct forming an initialsedimentation path of the heavy fraction of the fed goods, and alongwhich path the goods are pre-sorted into a bottom layer, rich with theheavy fractions, and a superposed layer, free of the heavy fractions;said duct mouth discharging the goods onto said goods supportintermediate the upper and lower ends of said goods support; the portionof said goods upport between said duct discharge mouth and said outletforming a succeeding sedimentation path for the heavy fraction of thegoods charged onto said goods support; said duct mouth being coplanarwith said goods support.

6. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, in which the dischargedirection of the duct mouth is opposite to the direction of thedescending gradient extending from said outlet to said discharge device.

7. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, in which the dischargedirection of said ductmouth extends at an angle of not more than 90 tothe direction of the descending gradient from said outlet to saiddischarge device.

- 8. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, in which said duct has atleast one side wall separating the duct from the good support; said one7 side wall being formed with an overflow opening whose lower edge isspaced above the goods support, said overflow opening discharging towardthe goods support.

9. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, in which said duct formspart of said gaspermeable goods support and is bounded by side walls onsaid support.

10. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, in which said gas-permeablebottom of said duct has a gradient rising toward said outlet at least ina front region adjacent said duct mouth.

11. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 10, in which saidgas-permeable bottom of said duct has a descending gradient between thegoods receiving end of said duct and said front region.

12. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, in which said duct mouth isspaced from said discharge device by at least the length of saidsucceeding sedimentation path. I

13. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, including a casingenclosing said goods support and said vibrating duct; said meansdirecting gas upwardly through said support opening into said casingbeneath said support; a hood closing said casing above said goodssupport; and gas exhaust means opening through said hood.

14. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 13, in which said goodssupport with said duct is fixedly connected with said casing along itsperipheral edges.

15. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 14, in which said goodsfeeding device extends along one side of said goods support andsubstantially parallel to the gradient of said goods support; saidcasing having side walls; one side wall of said duct being formed by aside wall of said casing, and the other side wall of said duct beingformed by a partition.

16. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 14, in which said duct iscovered by said hood.

17. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 13, in which the exhaustopening through said hood comprises a tubular collar; a sleeve connectedto said collar and communicating therewith, said sleeve extendinglaterally from said collar; and means selectively operable to close saidsleeve.

18. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 13, in which said hoodincludes a transparent portion at least in the range of said outlet.

19. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, including a blast nozzle inthe range of said outlet and directing a gas blast in the direction ofthe descending gradient of said goods support and substantially parallelto said goods support.

20. In apparatus for separating granularv goods of different specificgravity, the improvement claimed in claim 5, in which said goods supportcomprises a screen; and a perforated plate beneath said screen andextending in spaced parallel relation thereto and controlling the gasvelocity through said goods support.

21. In apparatus for separating granular goods of different specificgravity, the improvement claimed inclaim 20, including baffles extendingbetween said screen and said perforated plate and bonded to eachthereof, said baffles sub-dividing the surface of said screen intopanels.

22. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, in which said goods supporthas side walls converging from said discharge device toward said outlet;said duct extending intermediate said side walls parallel to thelongitudinal center line of said goods support; and a wedge on saidgoods support between said duct and said outlet, the tapered end of saidwedge facing said duct mouth.

23. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 22, in which said goodssupport has a plane of symmetry; said duct and said wedge beingpositioned symmetrically with respect to the plane of symmetry of saidgoods support.

241 In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 23, including respectiveoutlets each in the range of the intersection of a respective wedgeflank with a respective side wall of said goods support.

25. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 22, in which each of saidconverging side walls forms, with a normal to the longitudinal centerline of said goods support, an angle whose tangent is at least equal to1.8, both angles being equal to each other.

26. In apparatus for separating granular goods of different specificgravity, the improvement claimed in 1 1 claim 22, in which the includedangle of the flanks of said wedge is equal to twice the angle ofinclination of each side wall of said goods support.

27. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 5, in which said goods supporthas lateral boundries extending from said discharge device toward saidoutlet, said lateral boundaries forming, with the normal tothelongitudinal center line of said support, an angle whose tangent isat least equal to 1.8.

28. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 27, in which the tangent ofsaid angle is between 2 and 3.

29. In apparatus for separating granular goods of different specificgravity, and of the type including an inclined gas-permeable goodssupport, means directing a gas current upwardly through, the support, anoutlet for the heavy fractions at one end of the support, a dischargedevice for the light fractions at the other end of the support, thesupport having a gradient which descendsafrom the outlet to thedischarge device and being vibrated in 'a direction opposite to thedescending gradient, and a goods feeding device discharging onto thegoods support: the improvement comprising, in combination, a vibratingduct, having a gas-permeable bottom and a discharge mouth, included insaid feeding device; means directing a gas current upwardly through saidgas-permeable bottom; said duct forming an initial sedimentation path ofthe heavy fraction of the fed goods, and along which path the goods arepre-sorted into a bottom layer, enriched with the heavy fractions,

and a superposed layer, free of the heavy fractions; said duct mouthdischarging the goods onto said goods support intermediate the upper andlower ends of said goods support in the form of said two layersmaintained in such superposed relation; the portion of said goodssupport between said duct discharge mouth and said outlet forming asucceeding sedimentation path for the heavy fraction of the goodscharged onto said goods support; said duct mouth being coplanar withsaid goods support; a casing enclosing said goods support and saidvibrating duct; said means directing gas upwardly through said supportopening into said casing beneath said support; a hood closing saidcasing above said goods support; and gas exhaust means opening throughsaid hood; said goods support with said duct being fixedly connectedwith said casing along its peripheral edges; said goods feeding deviceextending along one side of said goods support and substantiallyparallel to the gradient of said goods support; said cas- 7 ing havingside walls; one side wall of said duct being formed by a side wall ofsaid casing, and the other side wall of said duct being formed by apartition; said partition extending to said duct mouth, and being formedwith an overflow port between said duct mouth and said discharge device.

30. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim' 29, in which said over flowport has a bottom rectilinear edge inclined downwardly, in a directiontoward said outlet, relative to said goods support.

1. In a method of separating granular goods of different specificgravity, wherein the granular goods are separated, by a forced air flowtherethrough while the goods are on a goods support subjected to avibration, into a layer of heavier fractions and a layer of lighterfractions, the layers are separated, and the layers are separatelydischarged: the improvement comprising the steps of, in advance ofcharging the granular goods onto the support, pre-sorting the goods intoa bottom layer, enriched with the heavy fractions, and a superposedlayer, free of the heavy fractions; subsequently flowing the layeredpre-sorted material onto the support as a continuous current, with atleast the layer enriched with heavy fractions having a laminar flow; onthe support, separating the two layers to flow along the support insubstantially opposite respective directions; and separately dischargingeach layer.
 2. In a method of separating granular goods of differentspecific gravity, the improvement claimed in claim 1, including the stepof conducting the continuous current along a laterally confined pathwhich is coplanar with the goods support.
 3. In a method of separatinggranular goods of different specific gravity, the improvement claimed inclaim 1, including subjecting at least one of the fractions tosubstantially a reversal in flow direction when charged onto the goodssupport.
 4. In a method of separating granular goods of differentspecific gravity, wherein the granular goods are separated, by a forcedair flow therethrough while the goods are on a goods support subjectedto a vibration, into a layer of heavier fractions and a layer of lighterfractions, the layers are separated, and the layers are separatelydischarged: the improvement comprising the steps of, in advance ofcharging the granular goods onto the support, pre-sorting the goods intoa bottom layer, enriched with the heavy fractions, and a superposedlayer, free of the heavy fractions; maintaining such superposed relationwhile subsequently charging the two layers onto the goods support; thelayered pre-sorted material being flowed onto the support as acontinuous current, with at least the layer enriched with heavyfractions having a laminar flow; conducting the continuous current alonga laterally confined path which is coplanar with the goods support; andlaterally discharging at least a part of the superposed layer, free ofthe heavy fractions, from the path onto the goods support in advance ofthe discharge end of the path.
 5. In apparatus for separating granulargoods of different specific gravity, and of the type including aninclined gas-permeable goods support, means directing a gas currentupwardly through the support, an outlet for the heavy fractions at oneend of the support, a discharge device for the light fractions At theother end of the support, the support having a gradient which descendsfrom the outlet to the discharge device and being vibrated in adirection opposite to the descending gradient, and a goods feedingdevice discharging onto the goods support: the improvement comprising,in combination, a vibrating duct, having a gas-permeable bottom and adischarge mouth, included in said feeding device; means directing a gascurrent upwardly through said gas-permeable bottom; said duct forming aninitial sedimentation path of the heavy fraction of the fed goods, andalong which path the goods are pre-sorted into a bottom layer, rich withthe heavy fractions, and a superposed layer, free of the heavyfractions; said duct mouth discharging the goods onto said goods supportintermediate the upper and lower ends of said goods support; the portionof said goods upport between said duct discharge mouth and said outletforming a succeeding sedimentation path for the heavy fraction of thegoods charged onto said goods support; said duct mouth being coplanarwith said goods support.
 6. In apparatus for separating granular goodsof different specific gravity, the improvement claimed in claim 5, inwhich the discharge direction of the duct mouth is opposite to thedirection of the descending gradient extending from said outlet to saiddischarge device.
 7. In apparatus for separating granular goods ofdifferent specific gravity, the improvement claimed in claim 5, in whichthe discharge direction of said duct mouth extends at an angle of notmore than 90* to the direction of the descending gradient from saidoutlet to said discharge device.
 8. In apparatus for separating granulargoods of different specific gravity, the improvement claimed in claim 5,in which said duct has at least one side wall separating the duct fromthe good support; said one side wall being formed with an overflowopening whose lower edge is spaced above the goods support, saidoverflow opening discharging toward the goods support.
 9. In apparatusfor separating granular goods of different specific gravity, theimprovement claimed in claim 5, in which said duct forms part of saidgas-permeable goods support and is bounded by side walls on saidsupport.
 10. In apparatus for separating granular goods of differentspecific gravity, the improvement claimed in claim 5, in which saidgas-permeable bottom of said duct has a gradient rising toward saidoutlet at least in a front region adjacent said duct mouth.
 11. Inapparatus for separating granular goods of different specific gravity,the improvement claimed in claim 10, in which said gas-permeable bottomof said duct has a descending gradient between the goods receiving endof said duct and said front region.
 12. In apparatus for separatinggranular goods of different specific gravity, the improvement claimed inclaim 5, in which said duct mouth is spaced from said discharge deviceby at least the length of said succeeding sedimentation path.
 13. Inapparatus for separating granular goods of different specific gravity,the improvement claimed in claim 5, including a casing enclosing saidgoods support and said vibrating duct; said means directing gas upwardlythrough said support opening into said casing beneath said support; ahood closing said casing above said goods support; and gas exhaust meansopening through said hood.
 14. In apparatus for separating granulargoods of different specific gravity, the improvement claimed in claim13, in which said goods support with said duct is fixedly connected withsaid casing along its peripheral edges.
 15. In apparatus for separatinggranular goods of different specific gravity, the improvement claimed inclaim 14, in which said goods feeding device extends along one side ofsaid goods support and substantially parallel to the gradient of saidgoods support; said casing having side walls; one side wall of said ductbeing formed by a side wall of said casing, and the other side wall ofsaid dUct being formed by a partition.
 16. In apparatus for separatinggranular goods of different specific gravity, the improvement claimed inclaim 14, in which said duct is covered by said hood.
 17. In apparatusfor separating granular goods of different specific gravity, theimprovement claimed in claim 13, in which the exhaust opening throughsaid hood comprises a tubular collar; a sleeve connected to said collarand communicating therewith, said sleeve extending laterally from saidcollar; and means selectively operable to close said sleeve.
 18. Inapparatus for separating granular goods of different specific gravity,the improvement claimed in claim 13, in which said hood includes atransparent portion at least in the range of said outlet.
 19. Inapparatus for separating granular goods of different specific gravity,the improvement claimed in claim 5, including a blast nozzle in therange of said outlet and directing a gas blast in the direction of thedescending gradient of said goods support and substantially parallel tosaid goods support.
 20. In apparatus for separating granular goods ofdifferent specific gravity, the improvement claimed in claim 5, in whichsaid goods support comprises a screen; and a perforated plate beneathsaid screen and extending in spaced parallel relation thereto andcontrolling the gas velocity through said goods support.
 21. Inapparatus for separating granular goods of different specific gravity,the improvement claimed in claim 20, including baffles extending betweensaid screen and said perforated plate and bonded to each thereof, saidbaffles sub-dividing the surface of said screen into panels.
 22. Inapparatus for separating granular goods of different specific gravity,the improvement claimed in claim 5, in which said goods support has sidewalls converging from said discharge device toward said outlet; saidduct extending intermediate said side walls parallel to the longitudinalcenter line of said goods support; and a wedge on said goods supportbetween said duct and said outlet, the tapered end of said wedge facingsaid duct mouth.
 23. In apparatus for separating granular goods ofdifferent specific gravity, the improvement claimed in claim 22, inwhich said goods support has a plane of symmetry; said duct and saidwedge being positioned symmetrically with respect to the plane ofsymmetry of said goods support.
 24. In apparatus for separating granulargoods of different specific gravity, the improvement claimed in claim23, including respective outlets each in the range of the intersectionof a respective wedge flank with a respective side wall of said goodssupport.
 25. In apparatus for separating granular goods of differentspecific gravity, the improvement claimed in claim 22, in which each ofsaid converging side walls forms, with a normal to the longitudinalcenter line of said goods support, an angle whose tangent is at leastequal to 1.8, both angles being equal to each other.
 26. In apparatusfor separating granular goods of different specific gravity, theimprovement claimed in claim 22, in which the included angle of theflanks of said wedge is equal to twice the angle of inclination of eachside wall of said goods support.
 27. In apparatus for separatinggranular goods of different specific gravity, the improvement claimed inclaim 5, in which said goods support has lateral boundries extendingfrom said discharge device toward said outlet, said lateral boundariesforming, with the normal to the longitudinal center line of saidsupport, an angle whose tangent is at least equal to 1.8.
 28. Inapparatus for separating granular goods of different specific gravity,the improvement claimed in claim 27, in which the tangent of said angleis between 2 and
 3. 29. In apparatus for separating granular goods ofdifferent specific gravity, and of the type including an inclinedgas-permeable goods support, means directing a gas current upwardlythrough the support, an ouTlet for the heavy fractions at one end of thesupport, a discharge device for the light fractions at the other end ofthe support, the support having a gradient which descends from theoutlet to the discharge device and being vibrated in a directionopposite to the descending gradient, and a goods feeding devicedischarging onto the goods support: the improvement comprising, incombination, a vibrating duct, having a gas-permeable bottom and adischarge mouth, included in said feeding device; means directing a gascurrent upwardly through said gas-permeable bottom; said duct forming aninitial sedimentation path of the heavy fraction of the fed goods, andalong which path the goods are pre-sorted into a bottom layer, enrichedwith the heavy fractions, and a superposed layer, free of the heavyfractions; said duct mouth discharging the goods onto said goods supportintermediate the upper and lower ends of said goods support in the formof said two layers maintained in such superposed relation; the portionof said goods support between said duct discharge mouth and said outletforming a succeeding sedimentation path for the heavy fraction of thegoods charged onto said goods support; said duct mouth being coplanarwith said goods support; a casing enclosing said goods support and saidvibrating duct; said means directing gas upwardly through said supportopening into said casing beneath said support; a hood closing saidcasing above said goods support; and gas exhaust means opening throughsaid hood; said goods support with said duct being fixedly connectedwith said casing along its peripheral edges; said goods feeding deviceextending along one side of said goods support and substantiallyparallel to the gradient of said goods support; said casing having sidewalls; one side wall of said duct being formed by a side wall of saidcasing, and the other side wall of said duct being formed by apartition; said partition extending to said duct mouth, and being formedwith an overflow port between said duct mouth and said discharge device.30. In apparatus for separating granular goods of different specificgravity, the improvement claimed in claim 29, in which said over flowport has a bottom rectilinear edge inclined downwardly, in a directiontoward said outlet, relative to said goods support.